"You can easily make out word 'Yonkers' and 'York' on two different forms on the Tiahrt attack ad against Moran. Ooops," tweeted Chuck Todd, the NBC News political director.

Leading up to the Aug. 3 primary, Tiahrt and Moran have each tried to paint themselves as the most conservative candidate, and Moran has often said he is more in tune with Kansas voters.

Tiahrt campaign spokeswoman Michelle Schroeder said Moran was trying to change the subject and attempted “the oldest trick in the political book when you have no defense for your record.”

“The tax form could have been from any state in the nation because the numerous tax increases Congressman Moran has supported would affect every American,” Schroeder said.

Joe Aistrup, a Kansas State University professor of political science, said he didn't see the image of the New York tax forms used in the ad as a Tiahrt gaffe.

"The substance of the ad will be the thing people talk about. It clearly follows, if you will, the track of this campaign to the part of both these representatives to move themselves to be as far to the right as possible," Aistrup said. "And I think this ad is clearly pointed towards the tea party activists within the Republican party, who I think Tiahrt feels like he has the potential to gain their support."

Aistrup said the key will be how widespread the ad is played in the state, and he said part of it seemed to be telling that most of the votes referenced in the ad were Moran's votes in the 1990s as a state senator.

"It's clear they had to go scouring the record pretty far back to find these things," he said.

Tiahrt and Moran, two Republican congressmen from Kansas, are competing for the GOP nomination for the U.S. Senate seat currently held by Sam Brownback, a Republican running for governor.